The semilinear differential equation (1), (2), (3), in with , (a nonlinear wave equation) is studied. In particular for , the existence is shown of a weak solution , periodic with period , non-constant with respect to , and radially symmetric in the spatial variables, that is of the form . The proof is based on a distributional interpretation for a linear equation corresponding to the given problem, on the Paley-Wiener criterion for the Laplace Transform, and on the alternative method of...